Conventionally, there have been demands for achieving both a decrease in hazardous substances contained in the exhaust gas emitted from vehicles and an increase in gas mileage. In recent years, there have been further demands for reducing the load on the environment globally. Against this background, the development of electric vehicles has been promoted. Electric vehicles currently being developed or produced include, for example, a pure electric vehicle (PEV) equipped with a high capacity secondary battery, a hybrid electric vehicle (HEV) in which, for example, a gasoline engine and a high power secondary battery are combined, and further a fuel cell vehicle (FCV) in which, for example, a fuel cell and a high power secondary battery are combined. In any of these cases, the development of a high-efficiency motor is required. Such motors include driving motors, electricity generating motors, and electric charging motors. It also has been strongly demanded to stabilize the quality of the motors in terms of the running stability, in addition to an increase in efficiency. Especially, motors for electric vehicles are required to have excellent oil resistance at high temperatures as compared with motors for common vehicles. In order to improve the efficiency, motors for electric vehicles need to be in an ATF (automatic transmission fluid). Since the ATF may reach a high temperature, the motors are required to have resistance to high temperatures in the ATF.
Conventionally, it has been proposed to use multifilament yarns of polyphenylene sulfide (PPS) fibers as an electrical insulating material (Patent Document 1). Furthermore, it also has been proposed to use monofilament yarns of PPS fibers to produce a protective sleeve (see Patent Document 2). Moreover, for electric vehicles, a cylindrical flexible protective sleeve has been proposed that is produced by using both monofilaments and multifilaments with oil resistance at high temperatures (see Patent Document 3). A protective sleeve also has been proposed that has a cylindrical braided cord structure made of 4 to 50 filament yarns with a single-yarn fineness of 30 to 100 dtex (see Patent Document 4). Furthermore, a protective sleeve also has been proposed that has a cylindrical braided cord structure made of 4 to 30 filament yarns with a single-yarn fineness of 19 to 88 dtex (see Patent Document 5).
When a sleeve is produced using multifilaments of ordinary thickness with a single-yarn fineness of around 5 dtex, it cannot maintain its cylindrical shape and is deformed into a squashed flat shape. This results in difficulties to insert a copper wire into the sleeve, which has been a problem. Patent Document 2 mentioned above proposes a sleeve that is produced using monofilaments. In this case, the sleeve has a cylindrical shape but using the monofilaments alone results in a rough braided structure and thus voids due to their thick fibers. This results in poor electrical insulation properties, which has been a problem. In Patent Document 3, the present applicant proposed the use of both monofilaments and multifilaments. In this case, a sleeve with excellent workability, adequate flexibility, and good copper wire covering properties can be obtained. However, since two types of yarns that are greatly different in thickness of their single yarns from each other are braided, processing stability is an issue, including tautening. Furthermore, there is a problem that multifilaments whose fibers are thinner tend to be napped. Patent Documents 4 and 5 propose braided cords that maintain cylindrical shapes using multifilaments with higher single-yarn fineness.
On the other hand, motor and automobile manufacturers have been requesting a further improvement in electrical insulation performance of sleeves, but at the same time, there have also been demands for increasing the economic efficiency and reducing the weight and size of components.